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186                                LOTS  OF
bolclt's scientific acquirements, as they are collected by
Mm in " BZosmos/J we must omit Ms classification of
Tolcanos into central and connected ones., especially as
this system lias been introduced into science by other
naturalists. We will return to Hximboldtfs pecxiliar field,
and treat of Ms results on the creative and destructive
volcanic power, in reference to mountains and rocks.
TMs brings us to the extensive field of mineralogic
geognosy, on which  Humboldt always worked with
great predilection with  his old friend  Leopold  von
Buchj and  which treats of the formal  composition
and arrangement of the earth/s strata, and gradually
leads to the geograpMcal form  of its surface.    The
strata of the earth were to him the pages of a large
book in which he read  the events of the past; the
kinds and forms of rocks he interpreted as the great
characters of a history  of  creation   extending   over
many thousands of years.    He perceived the process
of the formation of mountains as fourfold.    He calls
the matter wliich has once been projected from the
interior of the earth in fluid masses, and which has
now become more or less solid, eruption rock;—that
matter wMch was contained in   the fluid in   small
particles,   and   has been   gradually  precipitated,   he
calls sediment rock, and includes among it the greater
part of the horizontal strata  of earth,  the so-called
tertiary groups,  which lie above the chalk formation,
^nd  contain fossil remains of mammalia,  Crustacea,
&c.    The transformed rocks are those   changed by
contact   with   volcanic or  precipitated   earth, or by
vaporous   exhalation  or absorption  of matters from
below, while by conglomerates he means the sand and
rock formation composed  of mechanically-separated
masses of the three other classes.    All these four spe-
cies Humboldt describes; as still progressing in their
formation, the action of fire and water, though not so
violent  as  formerly, is still  exercising its influence.
Among the first class, the eruption rock, Humboldt
includes granite and Syenite,* the quartz porphyries,
* A mixture of feldspar and  homblend, called after the town
of Syene,  in Upper Egypt.